Closed chamber drier including vertically spaced, horizontal roller conveyors and means for positively circulating drying gases upwardly through the conveyors and about the material supported on the conveyors



Ai 8, 1947- B. WILSON ,418,683

CLOSED CHAMBER DRIER INCLUDING TICALLY SPACED, HORIZONTAL I ROLLER CONVEYORS AND MEANS F POSITIVELY CIRCULATING DRY GAS UPWARDLY THROUGH THE CO YORS D AB THE IAL 5 01mm on THE may 'l edJ .13, 45

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FEWJWM ATTORNEY Patented Apr. 8, .1947

CLOSED CHAIWBER DRIER INCLUDING VER- TICALLY SPACED, HORIZONTAL ROLLER CONVEYORS AND MEANS FOR POSITIVELY CIRCULATING DRYING GASES UPWARDLY THROUGH THE CONVEYORS AND ABOUT THE MATERIAL SUPPORTED ON THE CON- VEYORS Broadus Wilson, Raleigh, N. C.

Application January 13, 1945, Serial No. 572,648

This invention relates to apparatus for drying. More particularly the invention deals with a drier of the enclosed-chamber type wherein the drying air is heated and re-circulated with only enough make-up air supplied to maintain the humidity thereof at or below the maximum necessary for over-all emciency. While by no means limited to such use, the invention is particularly intended for drying potatoes or other tubers.

One object of my invention is to provide a drier wherein the gases are circulated under positive pressure.

Another object is to provide a drier as in the immediately preceding paragraph wherein a portion of the drying gases are re-circulated and re-heated, while the remaining portion is exhausted to the atmosphere.

A further object is to provide a drier, wherein the articles to be dried are moved in successively lower substantially horizontal paths to and fro across a drying chamber, while the drying gases are positively circulated upwardly, under pressure differentials, over and about the transverselymoving articles.

A' still further object is to provide a drier of the closed chamber type, wherein make-up air is admitted through the charging and exit open ings, ducts being provided to lead make-up air adjacent said openings from points outside the building housing the drier, whereby drafts on the workers in said building are avoided.

A further object is to provide a drier of the type aforesaid, wherein the velocity and turbulence of the drying medium over and about the articles to be dried are increased by the conveyors themselves, as well as by the natural decrease in volume of the cooling drying medium and the positive pressure differentials and resulting circulation of the medium.

Other objects and advantages will become apparent as the description proceeds.

In the drawing:

Fig. 1 is a cross section through a preferred embodiment of my invention showing the arrangement of rollers and belts, the baffles for directing the articles to be dried in the desired path, the fan or blower for impelling the drying medium in a re-circulating path, the heating device, and the exhaust fan for withdrawing the shows the general path which the drying air takes in completely enevloping and encompassing each of the articles passing therethrough, where- 5 Claims. (Cl. 34207) by rapid and eflicient absorption of the surface moisture is assured.

Fig. 2 is a schematic view showing a modified arrangement for circulating the drying medium, wherein make-up air is admitted into the re-circulating duct just ahead of the main blower, while an equal amount of spent, or moistureladen drying medium is exhausted from the main duct leading from the chamber.

Fig. 3 is a schematic view, similar to Fig. 2 wherein fresh make-up air is conducted from an external source, to and adjacent the principal openings for admitting the same to the drying chamber, whereby drafts that would otherwise be caused by the entrance of make-up air through door, windows and other openings in the building are avoided.

Fig. 4 is a diagrammatic view similar to Figs. 2 and 3 showing the entrance of make-up air as in Fig. 2, and using the entrance and exit openings for the articles to be dried for exhaust passages.

Fig. 5 is a diagrammatic view, similar to Fig. 2 but using a separate duct without a fan, for exhausting moisture-laden air.

Figure 6 is a detail view, partly in section, of one end of one of the rollers and its pivotal belt mounting.

Referring now to the drawing wherein like reference characters are used to identify corre. sponding parts throughout, A indicates the drying chamber or housing and which, as shown, may be generally rectangular in cross section. As indicated at H, the top of the chamber has a flared opening connecting with a pipe or duct D through which the main volume of the drying medium is withdrawn. At I2, I have indicated in dotted lines the exhaust pipe or duct leading to the main fan or blower B which, as shown, may be of the centrifugal type. After leaving the fan, the drying medium is conducted through a pipe or duct M to an enlarged heating chamber C where it is heated, as by passing over and about coils I6. These coils may consist of tubing for conducting steam or other heated fluid, into heatexchanging relation with the drying medium. Furthermore, if desired in those cases where the articles to be dried are not deletericusly affected thereby, heating ma be accomplished by direct oilor gas-fired burners wherein the entire products of combustion are introduced into chamber C, mixed with the air by the natural turbulence of the moving gases and the resulting mixture of heatedgas. passed into the drying chamber. This procedure is to be preferred where, as aforesaid,

the articles to be dried are not harmed thereby, because of the high over-all eiliciency of the drier secured, it being obvious that large stock losses are thus eliminated.

After heating to, say, 150 F., the drying medium is forced into chamber A through flared opening or inlet I1 and, under influence of the pressure difierential between the inlet at IT, and exhaust'opening at I2, moves upwardly around and over the articles to be dried. 7

At E is indicated a conduit through which a portion of the drying medium is exhausted. The eifective area of this conduit may be controlled by a series of pivoted vanes I9, while the powerdriven fan 20 is provided to give positive and precise control at all times over the necessary portion of air to be exhausted.

In the embodiment selected for illustration, I have used a series of three endless conveyors. Each conveyor consists of a pair of endless belts, roller belts or chains 2| having a series of relatively closely spaced rollers 22 pivotally connected at opposite ends on studs or pins journaled in bearings carried by the respective belts, as is well known in the art. Each belt or chain is guided by a number of sprockets or pulleys 23 fixed to shafts 24 which, in turn are journaled in bearings, not shown, carried by the walls of chamber A. Preferably, these shafts extend transversely across the chamber whereby the pulleys or sprockets 23 thereon adjacent each side wall of the chamber are rotated synchronously. Also, at least one shaft of the pair guiding and actuating each respective belt, projects exteriorly of the chamber and is there mechanically connected with the projecting portions of the other shafts and with a suitable source of power, such as an electric motor, whereby the belts and rollers are moved in unison and in the proper directions, as will be subsequently explained. While the length and diameter of rollers 22 may be widely varied, depend.

ing upon the desired capacity of the drier, and the size or nature of the articles to be dried, rollers of about six feet in length and 2 in diameter are satisfactory for a drier intended for potatoes. The spacing of the rollers will, of course, depend upon their diameter and the minimum size of the articles to be dried.

In the preferred embodiment, of Fig. l, I have used three roller belts 2|, and it will be understood that their shafts 24 are so connected that the upper passes of the upper and lower belts pass from right to left, as viewed in said figure, while the upper pass of the middle or intermediate belt, passes from left to right.

The potatoes or other objects'to be dried, are introduced into the drying chamber through an opening la. This opening .is closed to the maximum'extent possible, by means of a mop or flap 25 which, while permitting free ingress of the articles, prevents the escape th'erethrough of any substantial amount of air or other drying medium.

' A plate or baffle 26 and an attached flap 21, guide the potatoes through opening Ill-a onto rollers 22. As they approach the other, or left end, of the upper conveyor, the articles pass through a mop 28 that is provided to prevent drying medium from passing around the adjacent end of the conveyor, and thence onto a bafii plate 29 that deflects them over and onto the rightwardly moving upper pass of the intermediate conveyor. After traversing th chamber on the intermediate conveyor, the potatoes or other articles pass through mops 30, supported by a bracket or baffle plate 3i whence they drop onto a baflle plate 32 and are thereby reflected onto the leftwardly moving pass of the lower conveyor and, after again traversing the chamber A, drop onto deflector plate 33. and pass from the drying chamber through exit l0b. In addition to the baflles 26, 29, 3!, 32 and 33 already mentioned, additional bailies 35 and 36 may be provided, each provided with a flap of flexible material, such as 21 attached to baffle 26. These flaps may be formed of sheet metal capable of being bent so that their free edges are closely adjacent, but out of contact with, the rollers. 22, whereby leakageof drying medium around the ends of the conveyors is negligible and substantially all of the heated drying gases are compelled to pass upwardly around and over the articles to be dried. If desired, a mop (not shown) similar to 25, 28 and 30, may be provided adjacent exit 10b .to substantially close this opening against the entrance of air while at the same time permitting description. A heat exchange medium is introduced into coils l6 and after the power means riving blower B, the conveyer belts 2i, and fan 20 are started, the potatoes or other articles I0 to be dried, are introduced at Illa at the proper rate depending upon the capacity of the machine, and are withdrawn in fully dried condition at I0b. Adjustment of damper or vanes l9 depends upon the moisture content of the articles when introduced. In general, the greater the surface moisture to be evaporated, the greater the amount of air necessary to be withdrawn through conduit E in order to keep the humidity of the re-cir culated gases at or below the permissible maximum.

Consideration of'the arrangement of my drier will show that the pressure gradient in the recirculating passage is negative or somewhat below atmospheric at the intake side of blower B and, of course, rises sharply as it passes through the blower. Therefore the pressure is above atmospheric as the gases pass through conduit l4 and heating chamber I6. From this point, the pressure gradient graduallydrops asthe gases. pass upwardly over and around the rollers and the articles thereon and pass through duct D and recirculating passageway or duct l2 to the entrance to the blower. Thus the pressure or the gases in chamber A is positive, or greater than at-;/ mospheric over most of the drying chamber; and decreases gradually from a maximum at the bottom to approximately atmospheric at the top.

Thus it will be apparent to those skilled in the art that my invention possesses many features contributing to high efflciency and a high rate of evaporation for the capacity of the machine. Firstly, the air at the entrance I! to the chamber, may, for example, be 150 F. or 609.6 abs., while at the time it leaves the chamber, the temperature has dropped to, say 70 F. or 529.6 abs. Since a pressure difference of a few inches of water only is utilized in the operation of the drier, the specific volumes may reasonably be I assumed to vary directly as the absolute temperatures. Thus there will be approximately a 13% decrease in volume in the drying gases as they pass through the drier.

Assuming the output of the blower as 15,000 c. f. m., the amount leaving the heater would be 15,000 1.13 or 16,950 0. f. m. With rollers' 6 feet in length, spaced one-half inch apart, and a total of rollers effective at any one time to V 15,0 00/25 .33 or 1818 feet per minute if other factors beside the cooling of the air by evaporation are disregarded. However, the exhaust blower 20 pulls about 4000 c. f. m. of drying gas,

approximately one-half of which may reasonably be assumed to come in through la and the other half through I012. This would give a surface velocity through the top loaded belt of 15,000 plus 2000, divided by 25X .33, or slightly more than the velocity through the bottom belt. The only assumption in this calculation is the division of make-up air between the two inlets and this can be controlled by the baflies at I Do.

Thus the surface velocity of the drying gases may remain substantially constant throughout their travel through the drying chamber. Inasmuch as the evaporating capacity per cubic foot of gas varies directly as the square of the velocity, other factors remaining constant, it will be clear that my drier utilizes the heat content of the drying gases in a very efiicient manner.

Secondly, it will be noted that the rollers 22 of the several conveyor belts substantially reduce the effective horizontal cross-sectional area of the drying chamber. As a result the velocity of the heated gases materially increases as they pass between the rollers. As the articles being dried will normally be supported between rollers. this increase in velocity, together with the positive pressure present throughout at least the main portion of the upward travel of the drying gases, assures that each potato is thoroughly and completely enveloped by the drying gases many times during its passage through the machine. In other words, while there is a conversion of static into velocity head of the gases as they pass between the rollers, the static head is always positive throughout the travel of the gases through the drying chamber, and. of course, the velocity head is immediately reconverted into static head. with slight loss. as soon as the gases have passed between the rollers and move into the spaces between passes of the conveyor belts.

Th1rdly. the rollers them elves act to increase the desirable turbulence of the gases.

In ad ition to the foregoing advanta es. I use rollers that are covered with a material having natural capillary attraction for water. While numerous such covering materials are known and will give good results. I have found that rollers covered with zinc oxide are especially eflicient. Thus, the covering of the rollers absorbs water from the objects be ng dried and this water tends to spread out over the entire surface of the rollers and is thus rapidly evaporated.

The exhaust fan 20 pulls in more than enough air to keep the velocity up. (Drying on the top run is slower due to colder air.)

In the species just described, the make-up air,

equal in volume to that withdrawn at E, may

enter through opening a and opening I 0b, whereby it. is assured that none of the dryin'g gases emerge into the room in which the drier is located.

In Fig. 2, I have shown a modification in which make-up air is introduced at F, at a point immediately adjacent the suction side of the blower,

and is withdrawn through a duct E branching from the recirculating pipe D. It will be understood that the entrance of air at F may be controlled by a damper, if desired, while withdrawal of a like amount of heated gases at E may be controlled by a fan 20 and vanes l9, as in the species of Fig. 1. Fan 20 may be used, depending upon whether or not the static pressure at the top of the drying chamber is suificiently above atmospheric and this condition will, in turn depend mainly upon the speed of blower B. In any given installation slight changes in speed of the blower may be effected to give the desired pressure values to assure smooth operation and precise control at all times.

At Fig. 3, I have showna modification which contemplates the admission of make-up air at the entrance I and exit 2, for the potatoes; and in order to preclude the creation of drafts otherwise caused by the necessary introduction through doors and windows of large quantities of make-up air into the room housin the drier, I provide ducts 3 and 4 extending from points outside the building and having theiropen ends terminating at points closely adjacent the exit opening 2 and entrance I.

Fig. 4 shows a modification wherein the makeup air enters at F adjacent the suction or intake side of the blower, while equal amounts of heated gases escape through openings I and 2. This is permissible under conditions where the drier is located under an open shed, where the escape of products of combustion of a direct-fired heater is not objectionable, or where heating is effected by steam pipes or other surface-type of heat exchanger. Where the escape of drying gases into the area immediatel adjacent the drier is objectionable I provide the modification shown in Fig. 5, providing an outlet E to conduct the used gases to a point remote from the drier, such as to the outside of the building housing the same. In

all species however, I retain the feature of the blower located immediately adjacent the lower or entrance side of the drier, whereby positive pressure exists throughout a large portion of the drying chamber so that the drying medium is at all times used with a high degree of efficiency,

While I have shown a drier using three endless belt conveyors, it will be understood that the invention is not so limited, but that within practicable limits, any number of conveyors may be used so long as each upper or effective pass of each conveyor is driven in a direction o posite to that of the next succeeding lower effective, or article-supporting pass. Furthermore, while the rollers 22 have been shown as cylindrical, they may be polygonal in cross section without departing from the principles of the invention and the term "roller as here used, is intended to cover all practicable cross-sectional forms thereof. While I have shown the embodiment of my invention as now preferred by me, numerous changes, alternations, and substitutions of equivalents will be obvious to those skilled in the art. Hence I do not wish to be limited to the precise construction disclosed butreserve all such changes and substitutions as fall within the scope of the subjoined claims.

Having now fully disclosed my invention, what I claim and desire to secure by Letters Patent is:

1. In a drier for fruits, vegetables, and other articles, means forming a chamber having a top, bottom and side walls, said top wall having an exhaust opening therein, said bottom having a central entrance opening for drying medium, an

7 odd number of endless conveyors mounted in superposed relation within said chamber, each conveyor having an upper pass adapted to receive and convey articles to be dried from one side of said chamber to the other, said conveyors being driven so that each moves in a direction opposite'to the conveyor immediately below, there being an opening in said chamber through the top portion of a first said side wall and through which said articles are introduced onto the upper pass of the upper conveyor, a brush-like element closing said opening against the egress of drying medium, there also being a second opening in the base of a second said side wall opposite said first wall and through which dried articles emerge after leaving the upper pass of the lowermost conveyor, combined bafiie and deflector plates carried by said chamber to deflect articles being dried from the upper pass of each conveyor onto the upper pass of the next succeeding lower conveyor and to direct the drying medium upwardly through said conveyors, there being an exit opening for drying medium extending through said top wall of said chamber, a recirculating duct connecting said exit and entrance openings, said 25 u ber duct having a fresh air inlet therein, powerdriven impeller means in said duct between said fresh air inlet and entrance opening, and heater coils within said duct between said impeller means and said entrance opening, each said conveyor comprising a pair of spaced belts mounted inside by side relation and mounting a series of spaced rollers therebetween, there being a space between the peripheries of successive rollers dium decreasing'to substantially atmospheric at through which drying medium may pass up- 35 wardly about fruits and vegetables to be dried resting therebetween,

2. A drier as specified in claim 1, the rollers of said conveyors being covered with a layer of zinc oxide.

3. A drier as specified in claim 1, said exhaust opening having vane means manually adjustable to vary the efiective area of said opening, and

power-driven fan means operable to exhaust drying medium from said chamber.

4. A drier as specified in claim 1, said impeller.-

means acting to introduce drying mediuminto said chamber under greater than atmospheric pressure, the pressure gradient of said drying mesaid exit opening.

5. A drier as specified in claim rollers of said conveyors being journaled at its ends on said belt. 1

BROADUS WILSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 1, each of said 

